Prostate cancer is the most common site of cancer in men in the United States with over 240,000 men diagnosed with prostate cancer in 2011. Over the past years, widespread prostate specific antigen (PSA) screening has resulted in the earlier detection of these cancers. Screening has also led to controversy as men with very early stage disease are being treated when it is not clear to what extent treatment may be of benefit to them. Many clinicians agree that early stage disease is being over treated and it is estimated that 27-56% of men who undergo treatment for early stage prostate cancer can be managed effectively with active surveillance (AS). Given the potential for significant side-effects (e.g., erectile dysfunction, urinary incontinence, and bowl irritation) associated with treatment, AS is an important and viable alternative for patients with low-grade disease. Physicians have noticed that psychological factors such as anxiety or certain disease and treatment related beliefs may be influencing men and their partners to select active treatment (AT) over AS. In addition, intimate partners often exert an important influence of treatment choice as they are the primary social support for cancer patients. These anecdotal observations are supported by theory (i.e., self- regulation theory) and reports in the literature. However, a systematic examination of the influence of these cognitive-affective and social factors on the decision to decide on and adhere to an AS regimen is missing. The present application aims to investigate the decision making process for AS using a theory-guided self- regulation approach focusing on cognitive, affective and social/partner factors. This will be the first comprehensive examination of the contribution of affective and cognitive processes to decision making for AS. It will also be the first in this literature to include the perspective of patients' partners on decision making through the use of qualitative and quantitative data collection methods. Thus, the specific aims are: 1) to explore the cognitive and affective treatment decision-making processes among prostate cancer patients who are eligible for active surveillance and their partners/close allies. Aim 2: To explor how patients arrived at their decision and to investigate the influence partners/close allies play in this process. PUBLIC HEALTH RELEVANCE: Prostate cancer is the most common site of cancer in men in the United States with over 240,000 men diagnosed with prostate cancer in 2011. Over the past years, widespread prostate specific antigen (PSA) screening has resulted in the earlier detection of these cancers. Screening has also led to controversy as men with very early stage disease are being treated when it is not clear to what extent treatment may be of benefit to them. Many clinicians agree that early stage disease is being over treated and it is estimated that 27-56% of men who undergo treatment for early stage prostate cancer can be managed effectively with active surveillance (AS). Given the potential for significant side-effects (e.g., erectile dysfunction, urinary incontinence, and bowl irritation) associated with treatment, AS is an important and viable alternative for patients with low-grade disease. This study will explore the affective and cognitive decision making processes in men eligible for AS.